Advances in the FTU collective Thomson scattering system.

The new collective Thomson scattering diagnostic installed on the Frascati Tokamak Upgrade device started its first operations in 2014. The ongoing experiments investigate the presence of signals synchronous with rotating tearing mode islands, possibly due to parametric decay processes, and phenomena affecting electron cyclotron beam absorption or scattering measurements. The radiometric system, diagnostic layout, and data acquisition system were improved accordingly.

Mutual interaction of Faraday rotation and Cotton–Mouton phase shift in JET polarimetric measurements.

The paper presents a study of Faraday rotation (FR) angle and Cotton–Mouton (CM) phase shift measurements to determine their mutual interaction and the validity of the linear models presently used in equilibrium codes. Comparison between time traces of measurements and model calculations leads to the result that only an exact numerical solution of Stokes equations can reproduce in all the experimental data. As a consequence, approximated linear models can be applied only in a limited range of plasma parameters.

A new calibration code for the JET polarimeter.

An equivalent model of JET polarimeter is presented, which overcomes the drawbacks of previous versions of the fitting procedures used to provide calibrated results. First of all the signal processing electronics has been simulated, to confirm that it is still working within the original specifications. Then the effective optical path of both the vertical and lateral chords has been implemented to produce the calibration curves.

Investigating the possibility of a monitoring fast ion diagnostic for ITER.

In burning plasma fusion devices, fast ion transport plays a central role in the performances of the machines. Moreover the losses of energetic particles might cause severe damages on plasma facing components. Therefore real time measurements of fast ion transport would provide valuable information for safe and reliable plasma operations.

Evolution of the millimeter-wave collective Thomson scattering system of the high-field tokamak Frascati Tokamak Upgrade.

We first describe the improved receiving system of the diagnostic experiment of millimeter-wave collective Thomson scattering being run on the Frascati Tokamak Upgrade (FTU), and then discuss some peculiar problems and new operating procedures related to the investigation of strong anomalous spectra of nonthermal origin, many-orders-of-magnitude stronger than the ion thermal feature merged in them, systematically observed in the experimentation, and finally ascribed to a perturbation of the gyrotron that generates the probing beam. Arguments in favor of a more general valence of the solutions actuated for the specific case of FTU are finally given.

Thomson-scattering diagnostic on the Frascati tokamak upgrade.

The Frascati tokamak upgrade Thomson-scattering system is used for the measurement of electron-temperature and electron-density spatial profiles along the vertical diameter of the tokamak at 19 spatial points up to 10 times in a single plasma discharge, with a spatial resolution that ranges from 2 cm in the central region to 4 cm in the plasma edge. The radiation source is a Nd:YLF laser that operates at 1053 nm, with a divergence of 0.4 mrad full angle, and is capable of delivering a burst of 10 pulses with energies of 4.

Evidence for multistability of light solitons in SF(6) absorption measurements.

We report experimental evidence of the multistability of reshaped pulses that are observed when a 1.5-nsec CO(2)-laser pulse interacts with a pure SF(6) absorber. The data demonstrate that the dependence of the reshaped pulse delay on peak power is not a single-valued function under various experimental conditions.